1. Field of the Invention
The present invention relates to a catalytic converter suitable for use in controlling automotive exhaust emissions, and a method of controlling automotive exhaust emissions.
2. Description of the Related Art
Catalytic converters for use in controlling automotive exhaust gas must have a predetermined temperature or above when operated so as to make its catalyst do catalytic action. Hence, the catalyst must be heated when the temperature thereof is not sufficiently high, i.e., at the beginning of running of a vehicle.
Such techniques for heating the catalyst have been proposed in, for example, Japanese Utility Model Laid-Open No. 67609/1988. This disclosed technique is a method of operating a catalytic converter comprised of a metal monolithic catalyst disposed upstream of and adjacent to a main ceramic monolithic catalyst. The metal monolithic catalyst comprises an electrically conductible metal substrate with alumina coated thereon
However, deterioration of the catalyst such as a monolithic catalyst starts with that located upstream. In the catalytic converter disclosed in Japanese Utility Model Laid-Open No. 67609/1988, the catalytic component in the metal monolith catalyst, which is a preheater disposed upstream of and adjacent to the main monolithic catalyst, therefore deteriorates first, thereby reducing its exhaust gas conversion efficiency when the temperature of the exhaust gas is low. Furthermore, there is a possibility of the metal substrate being corroded.
The present inventors have found out through intensive studies that the aforementioned problems could be solved by causing an exhaust gas whose temperature is low to flow through a preheater and by switching over the flow passage of the exhaust gas from the preheater to a main catalyst when the temperature of the exhaust gas is raised to a predetermined value.